Seismic surveying is used for identifying subterranean elements, such as hydrocarbon reservoirs, fresh water aquifers, gas injection reservoirs, and so forth. In performing seismic surveying, seismic sources are placed at various locations above an earth surface or sea floor, with the seismic sources activated to generate seismic waves directed into the subterranean structure. Examples of seismic sources include explosives, air guns, or other sources that generate seismic waves.
The seismic waves generated by a seismic source travel into the subterranean structure, with a portion of the seismic waves reflected back to the surface for receipt by seismic receivers (e.g., geophones, hydrophones, etc.). These seismic receivers produce signals that represent detected seismic waves. Signals from seismic receivers are processed to yield information about the content and characteristic of the subterranean structure.
In addition to reflecting from subterranean elements in the subterranean structure, seismic waves can also reflect from a surface (such as a land surface or a sea surface). A seismic wave reflected from the surface is referred to as a surface-related multiple. In a marine environment, a sea surface is present, such that an air-water interface is present. Seismic waves can travel toward the air-water interface, and is reflected back from the air-water interface. In fact, there can be multiple reflections between the air-water interface and the sea floor. The reflected seismic waves that are due to reflection from the sea floor and the reflections from the air-water interface are referred to as surface-related multiples. In land-based applications, surface-related multiples can also be present, caused by multiple reflections between a land surface and a subsurface reflector that are received by a seismic receiver.
Surface-related multiples are generally considered to adversely affect accuracy of seismic processing and interpretation. Conventional techniques attempt to attenuate the surface-related multiples prior to performing seismic waveform inversion. Seismic waveform inversion refers to the process of producing a model of the subterranean structure that minimizes the difference (residuals) between observed seismic data (collected from seismic receivers) and calculated seismic data (calculated from a model).
Attenuating the surface-related multiples from observed seismic data is a pre-processing task that is labor-intensive and computing-intensive. Having to perform the pre-processing task to attenuate surface-related multiples can result in increased processing times for performing waveform inversion.